Production of biocrude oils from various bio-feedstocks through hydrothermal liquefaction: Comparison of batch and continuous-flow operations

Laboratory- and pilot-scale hydrothermal liquefaction (HTL) of biomass has predominantly been carried out in batch reactor systems. However, the development of continuous-flow reactor systems is critical for industrial deployment of HTL technology in a cost-competitive manner. In this study, a continuous-flow HTL system (with a feed capacity up to 6 kg/h) was developed and employed to convert various types of bio-feedstocks (wood sawdust, cornstalk, and black liquor) into biocrudes in the presence of K2CO3 catalyst at 300 °C for 12 min. The produced biocrude oils were characterized in detail by using GC-MS, FT-IR, GPC, and elemental analysis. This work compared the performance of the continuous-flow HTL process with that of a batch HTL process under the same conditions in terms of the yields and chemistry of the biocrude products as well as the energy recovery potential. The results indicated that HTL of different bio-feedstocks, particularly cornstalk and pinewood, in the continuous-flow reactor led to a higher yield of biocrude (32.4 and 34.5 wt %, respectively) with lower molecular weights and less solid residue (2.9 and 4.6 wt%, respectively) as well as a higher energy recovery rate (53.3 and 52.0%, respectively) compared with those in the batch reactor (Cornstalk: 23.8 wt%, 6.2 wt% and 46.5%; Pinewood: 28.5 wt%, 10.3 wt% and 50.8%, respectively). These promising results shall advance the future development and deployment of the HTL technology in Canadian and global bioenergy sectors.